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MEDIUM: stick-table: make stksess_kill_if_expired() avoid the exclusive lock
stream_store_counters() calls stksess_kill_if_expired() for each active counter. And this one takes an exclusive lock on the table before checking if it has any work to do (hint: it almost never has since it only wants to delete expired entries). However a lock is still neeed for now to protect the ref_cnt, but we can do it atomically under the read lock. Let's change the mechanism. Now what we do is to check out of the lock if the entry is expired. If it is, we take the write lock, expire it, and decrement the refcount. Otherwise we just decrement the refcount under a read lock. With this change alone, the config based on 3 trackers without the previous patches saw a 2.6x improvement, but here it doesn't yet change anything because some heavy contention remains on the lookup part.
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@ -198,15 +198,22 @@ static inline int __stksess_kill_if_expired(struct stktable *t, struct stksess *
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static inline void stksess_kill_if_expired(struct stktable *t, struct stksess *ts, int decrefcnt)
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{
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HA_RWLOCK_WRLOCK(STK_TABLE_LOCK, &t->lock);
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if (decrefcnt)
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ts->ref_cnt--;
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if (t->expire != TICK_ETERNITY && tick_is_expired(ts->expire, now_ms)) {
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HA_RWLOCK_WRLOCK(STK_TABLE_LOCK, &t->lock);
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if (decrefcnt)
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ts->ref_cnt--;
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if (t->expire != TICK_ETERNITY && tick_is_expired(ts->expire, now_ms))
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__stksess_kill_if_expired(t, ts);
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HA_RWLOCK_WRUNLOCK(STK_TABLE_LOCK, &t->lock);
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HA_RWLOCK_WRUNLOCK(STK_TABLE_LOCK, &t->lock);
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}
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else {
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if (decrefcnt) {
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HA_RWLOCK_RDLOCK(STK_TABLE_LOCK, &t->lock);
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HA_ATOMIC_DEC(&ts->ref_cnt);
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HA_RWLOCK_RDUNLOCK(STK_TABLE_LOCK, &t->lock);
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}
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}
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}
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/* sets the stick counter's entry pointer */
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@ -103,9 +103,9 @@ void stksess_free(struct stktable *t, struct stksess *ts)
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dict_entry_unref(&server_key_dict, stktable_data_cast(data, std_t_dict));
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stktable_data_cast(data, std_t_dict) = NULL;
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}
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HA_RWLOCK_WRLOCK(STK_TABLE_LOCK, &t->lock);
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HA_RWLOCK_RDLOCK(STK_TABLE_LOCK, &t->lock);
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__stksess_free(t, ts);
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HA_RWLOCK_WRUNLOCK(STK_TABLE_LOCK, &t->lock);
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HA_RWLOCK_RDUNLOCK(STK_TABLE_LOCK, &t->lock);
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}
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/*
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